1. Field of the Invention
The present invention relates generally to implants and, more particularly, to implants provided with bactericidal coatings so as not only to improve their antimicrobial properties, but also to make the implants fight germinating bacteria in situ.
2. The Prior Art
In a related co-pending application Ser. No. 07/663,361, filed Mar. 1, 1991, now abandoned, of Mohammed Farivar and Piran Sioshansi, entitled "Metallized Polymeric Implants, Methods and Apparatus," and assigned to a common assignee, Spire Corporation, Bedford, Mass., there are disclosed and claimed surface metallized polymeric implants, a method and an apparatus to improve the implants' biocompatibility and to reduce infusion-associated phlebitis and infection, twin commendable goals pulling in opposing direction. The disclosure of said application Ser. No. 07/663,361 is incorporated herein by reference.
For, efforts directed at fighting infection, the overriding consideration of this invention, does of necessity reduce biocompatibility. The balancing of these two goals is a delicate test facing the medical practitioner.
In applications where the implant is intended for relatively short dwell time within the body, in particular in the use of external fixation devices to immobilize a broken limb while it heals, infection-fighting ability of the device becomes paramount at the expense of biocompatibility. This is what is addressed by this invention.
Infections, such as nosocomial infections (infections originating in a hospital), result from polymeric, metallic and/or ceramic implanted devices, including external fixation devices, indwelling urological catheters and the like, being placed in the body. Medical device manufacturers have not employed bacteriostatic compounds as antimicrobial agents in such indwelling devices because of the difficulties associated with producing an adherent, long lasting film on such polymeric, metallic and/or ceramic surfaces. It has been noted that using ion-beam-assisted deposition technique (IBAD), well-adhering, ductile thin films of bacteriostatic/fungistatic compounds also can be applied to biomedical products.
The common assignee herein, Spire Corporation of Bedford, Mass., has been one of the pioneers in the field of ion beam technology. A plasma-supported ion beam technique for coating industrial cutting tools with a thin layer of cubic boron nitride to improve the tools' cutting properties is disclosed in U.S. Pat. No. 4,440,108, of Roger G. Little et al, granted Apr. 3, 1984, and assigned to said Spire Corporation. A plasma-ion deposition process of large-grain, thin semiconductor films directly on low-cost amorphous substrates is disclosed in U.S. Pat. No. 4,443,488, also of Roger G. Little et al, granted Apr. 17, 1984 and assigned to said Spire Corporation. A process of preventing surface discoloration in titanium orthopaedic implants by ion implantation is disclosed in U.S. Pat. No. 4,693,760 of Piran Sioshansi granted Sep. 15, 1987 and assigned to said Spire Corporation. An ion implantation process for plastics to enhance their surface hardness and their resistance to chemical attack is disclosed in U.S. Pat. No. 4,743,493 of Piran Sioshansi et al, granted May 10, 1988 and assigned to said Spire Corporation. A process for passivating the electrochemically active surface of metal alloys so as to inhibit their corrosion is disclosed in U.S. Pat. No. 4,743,308 of Piran Sioshansi et al, granted May 10, 1988 and assigned to said Spire Corporation. A sputter-enhanced ion implantation process, primarily of ball bearings, without the use of a separate evaporation system is disclosed in U.S. Pat. No. 4,855,026 of Piran Sioshansi, granted Aug. 8, 1989 and assigned to said Spire Corporation. An improved method and apparatus for the uniform ion implantation of spherical surfaces, such as ball bearings, is disclosed in U.S. Pat. No. 4,872,922 of Stephen N. Bunker et al, granted Oct. 10, 1989 and assigned to said Spire Corporation. A method of depositing an ionized cluster on a substrate is disclosed in U.S. Pat. No. 4,152,478 of Toshinori Takagi, granted May 1, 1979. And a method of coating a substrate with a stoichiometric compound is disclosed in U.S. Pat. No. 4,281,029 of Toshinori Takagi et al, granted Jul. 28, 1981. The use of ion beam processing is thus well known and widespread.